[Bug tree-optimization/127645] [16/17 Regression] wrong code at -O2

[pinskia at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=127645

Drea Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
      Known to fail|                            |11.1.0

--- Comment #5 from Drea Pinski <pinskia at gcc dot gnu.org> ---
The invalid undefined transformation in cselim started in GCC 11.
Most likely r11-897-g54ecfb182bc321 .

PRE turns (that happened in GCC 11 also):

  # .MEM_18 = VDEF <.MEM_13>
  MEM <union u0> [(void *)&g18].f2 = cstore_17;
  # VUSE <.MEM_18>
  _4 = g18.f1;

into:

  # cstore_17 = PHI <1(5), cstore_16(6)>
  # .MEM_18 = VDEF <.MEM_13>
  MEM <union u0> [(void *)&g18].f2 = cstore_17;
  _15 = VIEW_CONVERT_EXPR<unsigned char>(cstore_17);


Looks like jump threading then comes along and optimizes things (based on the
undefinedness it seems).